An example for such a burst transmission system is the handheld enhancement of the DVB (Digital Video Broadcasting) system. The DVB-H enhancements to the DVB-T (Digital Video Broadcasting Terrestrial) specifications include a forward error correction computed across the data section of a burst. The forward error correction code is placed in the error protection section of the same burst over which data section the error protection code has been computed. An example of such forward error correction is implemented in DVB-H as well as DVB-SH. The DVB-H as well as the DVB-SH (DVB satellite to handheld) both implement the multi-protocol encapsulation. The multi-protocol encapsulation (MPE) encapsulates multiple types of data, especially IP (Internet Protocol) datagrams into the data section of a burst. DVB-H/SH also implements the MPE-FEC (Multi Protocol Encapsulation-Forward Error Correction). MPE-FEC is the link layer error protection of DVB-H and DVB-SH. MPE-FEC provides intra burst data protection. A MPE-FEC frame is a matrix of 255 columns and a variable number of rows, e. g. 256, 512, 768, or 1024. Each element in the matrix of the MPE-FEC frame represents a byte. An MPE-FEC frame is an example of a burst. The first 191 columns of the MPE-FEC contain the IP datagrams that will be transmitted. This portion is the data section of the burst and is also called application data table (ADT). The rest of the 64 columns are dedicated to the forward error correction (FEC) generated by for example an eraser code, such as Reed Solomon, LDPC (Low Density Parity Check Code), etc. The FEC is contained in the error protection section of the burst. The FEC is also called RSDT (Reed Solomon Data Table) or inner-FEC. The inner-FEC is computed over the rows of the metrics ADT. It involves 1 D error correction, which is for example a FEC computed on each row of the ADT metrics. The redundancy created by the inner-FEC protects the loss of one datagram in one burst. Thus, the inner-FEC can insure an intra burst protection.
In a wireless network, such as DVB-H, DVB-SH, WiMAX (Worldwide Interoperability for Microwave Access), 3G/LTE (3rd Generation Long Term Evolution), end users have different requirements in terms of latency video visual quality, processing capabilities and power. It is thus a challenge especially for broadcast services to design a delivery mechanism that not only achieves efficiency in network bandwidth but also meets the heterogeneous requirement and capacities of the end users. To address the above challengers the different quality of service requirements in all components of a media delivery system from end to end should be supported simultaneously. Examples of such media delivery systems are voice service, http services etc.
Another example of such a media delivery system is a video delivery system which transmits scalable encoded video. Scalable video encoding is an advantageous way to meet the needs to achieve efficiency in network bandwidth and also to meet the heterogeneous requirement and capacities of the end users. In scalable video coding the signal is separated into multiple layers. The layers have different priorities. The base layer is the layer of highest priority. It can be independently decoded and provides basic video quality. The base layer must be robust to be received by users over all the network, what ever the radio conditions or the radio link quality might be. The enhancement layers can only be decoded together with the base layer and further increase the video quality and/or the video basic special and temporal resolution. The base layer in connection with the enhancement layer or enhancement layers provide video with the enhanced quality. Each terminal decodes at least the base layer and a number of enhancement layers that is linked to the capabilities of the terminal. Using scalable video layers allows networks providing multimedia broadcast and multicast services to adapt efficiently to the variability of the radio conditions, e. g. variable carrier to interference ratio or signal to noise ratio. It allows to optimise the usage of the radio resources using modulation and coding schemes leading to higher spectrum efficiency. Terminals experiencing bad radio link quality for example decode only the base layer, e. g. typically users at the edge of a cell for example. The base layer must be enough robust to be received by users all over the network or cell what ever the radio conditions or the radio link quality are. This can be achieved by choosing an adequate modulation and coding scheme. The enhancement layers are decoded only even the radio link quality is good, e. g. typically users near the antenna. The enhancement layer or the enhancement layers are differently protected than the base layer. They are usually less protected than a base layer e. g. by using a less robust modulation and coding scheme but leading to higher radio data rate.
In the document “Multi burst sliding encoding (MBSE)” of Luc Ottavj, Antoine Clerget, Amine Ismail, which was presented during a technical working group within the DVB-SSP (DVB satellite service to portable devices) standardization, an outer-FEC algorithm is presented which extends the intra-burst protection to an inter-burst protection, so that complete burst losses may be recovered. In order to achieve this, data coming from several bursts are interleaved before FEC protection is applied.
In the US patent application 2006/0262810 A1 a method for providing error protection to data packets in a burst transmission system is described. Error protection is provided unequally with respect to priority levels of the data packets. The error protection provided is inserted within one burst, thus protecting the loss of one data packet in one burst. The unequal error protection provided calculates the error protection code over the data section of one burst and puts the calculated error code in the error protection section of said same burst.
The object of the invention is to provide a method for providing unequal error protection to data packets in a burst transmission system with extended protection. Another object of the invention is to provide a burst transmission system with unequal error protection for data packets with extended protection.